_config.Configuration.PluginRespositories not instantiated causing InstallationManager.cs to crash with a null pointer.

MediaBrowser.Model/Configuration/ServerConfiguration.cs

@@ -270,6 +270,8 @@ namespace MediaBrowser.Model.Configuration
             IgnoreVirtualInterfaces = false;
             EnableSimpleArtistDetection = false;
 
+            PluginRepositories = new List<RepositoryInfo>();
+
             DisplaySpecialsWithinSeasons = true;
             EnableExternalContentInSuggestions = true;